Cosmological Imprint of an Energy Component with General Equation of
  State

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Abstract

We examine the possibility that a significant component of the energy density of the universe has an equation-of-state different from that of matter, radiation or cosmological constant (\(\Lambda\)). An example is a cosmic scalar field evolving in a potential, but our treatment is more general. Including this component alters cosmic evolution in a way that fits current observations well. Unlike \(\Lambda\), it evolves dynamically and develops fluctuations, leaving a distinctive imprint on the microwave background anisotropy and mass power spectrum.

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Structure formation with a self-tuning scalar field

Pedro Ferreira, Michael Joyce (1997)

A scalar field with an exponential potential has the particular property that it is attracted into a solution in which its energy scales as the dominant component (radiation or matter) of the Universe, contributing a fixed fraction of the total energy density. We study the growth of perturbations in a CDM dominated \(\Omega=1\) universe with this extra field, with an initial flat spectrum of adiabatic fluctuations. The observational constraints from structure formation are satisfied as well, or better, than in other models, with a contribution to the energy density from the scalar field \(\Omega_\phi \sim 0.1\) which is small enough to be consistent with entry into the attractor prior to nucleosynthesis.

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The Imprint of Gravitational Waves on the Cosmic Microwave Background

P. Steinhardt, R L Davis, J. R. Bond … (1993)

Long-wavelength gravitational waves can induce significant temperature anisotropy in the cosmic microwave background. Distinguishing this from anisotropy induced by energy density fluctuations is critical for testing inflationary cosmology and theories of large-scale structure formation. We describe full radiative transport calculations of the two contributions and show that they differ dramatically at angular scales below a few degrees. We show how anisotropy experiments probing large- and small-angular scales can combine to distinguish the imprint due to gravitational waves.